The most frequent heart disease is ischemia due to an at least partial occlusion (stenosis) of a coronary artery. Occlusion of a coronary artery may lead to a deficit in the perfusion of myocardial tissue. Various imaging modalities may be used to obtain data on the perfusion, e.g., MRI, PET, SPECT, CT, etc.
For example, cardiac MRI allows quantification of myocardial perfusion. In particular, first pass enhancement cardiac MRI may be used to assess the severity of perfusion deficits caused by coronary artery occlusions. In first pass enhancement cardiac MRI the uptake of a contrast agent in the myocardial tissue after the first pass of a contrast bolus is measured.
The contrast agent highlights the perfusion in the tissue. This procedure is often performed at rest and under stress, as perfusion deficits are often stress-induced. The stress may be induced by pharmacological agents that increase the heart rate. The contrast agent causes opacification, which is visible in the measured images, such as myocardial images. Typically, opacification is measured in gray-scale units from the video intensity on recorded images.
The measurement of the uptake of the contrast agent results in time-intensity curves. A time-intensity curve relates time, e.g., the time elapsed since the onset of the bolus passage, to the intensity of the uptake, e.g., at a particular location, or to the average intensity of the uptake at a particular segment, etc.
The quantification of myocardial perfusion can be a semi-quantitative or a true-quantitative analysis of the time-intensity curves. Semi-quantitative analysis includes the quantification of several characteristics of time-intensity curves, e.g., peak intensity, maximum up slope, mean transit time of the bolus passage, etc. In true quantitative analysis, the actual myocardial blood flow is calculated from a mathematical analysis of the arterial input function and the time-intensity curves obtained in the myocardium. A review of both semi-quantitative and true quantitative approaches is given in, e.g., M. Jerosh-Herold et al., “Analysis of myocardial perfusion MRI”, JMRI 19(6):758-770, 2004. Note that time-intensity curves can be obtained from various imaging modalities.
Results from these analyses can be presented using various visualizations. For example, one or more of the time-intensity curves may be graphed. The time-intensity curves may also be visualized using, e.g., bulls eye plots, color overlays and perfuseograms. Perfuseograms are described, e.g., in US patent application 2005/0124861: “Cardiac Perfusion analysis”, which is incorporated herein by reference.
European patent application EP1236177: “Automatic analysis of anatomical images time sequence”, describes an apparatus for treating medical images. The apparatus allows the automatic segmentation of cardiac images. For each segment the apparatus can determine time/intensity curves. The time/intensity curves can be analyzed by computing, per segment, some parameters, including the trend of the concentration of the intravascular contrast medium in the organ tissues.